Collision resolution for pucch scheduling requests

ABSTRACT

Collision mitigation for scheduling requests, SRs, on the physical uplink control channel, PUCCH, in Long Term Evolution, LTE, radiocommunication systems is described. Various types of SR collision mitigation information can be transmitted from a base station eNodeB ( 32 ) to a user equipment, UE( 36 ). The UE can use the collision mitigation information to determine how to transmit its SRs. The network or base station ( 32 ) can use its knowledge of the SR collision mitigation information sent to various UEs ( 36 ) (and/or additional information) to resolve SR collisions on the uplink.

TECHNICAL FIELD

The present invention relates generally to telecommunications systems,and in particular, to methods, systems, devices and software forcollision resolution for uplink scheduling requests, e.g., on the PUCCH.

BACKGROUND

Radio communication networks were originally developed primarily toprovide voice services over circuit-switched networks. The introductionof packet-switched bearers in, for example, the so-called 2.5G and 3Gnetworks enabled network operators to provide data services as well asvoice services. Eventually, network architectures will likely evolvetoward all Internet Protocol (IP) networks which provide both voice anddata services. However, network operators have a substantial investmentin existing infrastructures and would, therefore, typically prefer tomigrate gradually to all IP network architectures in order to allow themto extract sufficient value from their investment in existinginfrastructures. Also to provide the capabilities needed to support nextgeneration radio communication applications, while at the same timeusing legacy infrastructure, network operators could deploy hybridnetworks wherein a next generation radio communication system isoverlaid onto an existing circuit-switched or packet-switched network asa first step in the transition to an all IP-based network.Alternatively, a radio communication system can evolve from onegeneration to the next while still providing backward compatibility forlegacy equipment.

One example of such an evolved network is based upon the UniversalMobile Telephone System (UMTS) which is an existing third generation(3G) radio communication system that is evolving into High Speed PacketAccess (HSPA) technology. Yet another alternative is the introduction ofa new air interface technology within the UMTS framework, e.g., theso-called Long Term Evolution (LTE) technology. Target performance goalsfor LTE systems include, for example, support for 200 active calls per 5MHz cell and sub 5 ms latency for small IP packets. Each new generation,or partial generation, of mobile communication systems add complexityand abilities to mobile communication systems and this can be expectedto continue with either enhancements to proposed systems or completelynew systems in the future.

LTE uses orthogonal frequency division multiplexing (OFDM) in thedownlink and discrete Fourier transform (DFT)-spread OFDM in the uplink.The basic LTE downlink physical resource can thus be seen as atime-frequency grid as illustrated in FIG. 1, where each resourceelement corresponds to one OFDM subcarrier during one OFDM symbolinterval. In the time domain, LTE downlink transmissions are organizedinto radio frames of 10 ms, each radio frame consisting of tenequally-sized subframes of length T_(subframe)=1 ms as shown in FIG. 2.

Furthermore, the resource allocation in LTE is typically described interms of resource blocks, where a resource block corresponds to one slot(0.5 ms) in the time domain and 12 contiguous subcarriers in thefrequency domain. Resource blocks are numbered in the frequency domain,starting with 0 from one end of the system bandwidth. Downlinktransmissions are dynamically scheduled, i.e., in each subframe the basestation (typically referred to as an eNB in LTE) transmits controlinformation indicating to which terminals and on which resource blocksthe data is transmitted during the current downlink subframe. Thiscontrol signalling is typically transmitted in the first 1, 2, 3 or 4OFDM symbols in each subframe. A downlink system with 3 OFDM symbols asthe control region is illustrated in FIG. 3.

On the LTE uplink, single-carrier frequency division multiple access(SC-FDMA) is used in a manner wherein, as much as possible, thestructure is aligned as much as possible with the LTE downlink. Thus, asshown in FIG. 4( a), the uplink subcarrier spacing in the frequencydomain is also 15 kHz and resource blocks having 12 subcarriers are alsodefined for the LTE uplink. An example of the LTE uplink subframe andslot structure is shown as FIG. 4( b). Therein, it can be seen that onesubframe includes two equally sized slots, each slot having six or sevenSC-FDMA blocks (normal and extended cyclic prefix, respectively). Anexample of LTE uplink resource allocation is provided in FIG. 4( c),wherein the assigned uplink resource for a user corresponds to the sameset of subcarriers in the two slots.

The 3GPP LTE radio access standard has been written in order to supporthigh bitrates and low latency both for uplink and downlink traffic. Alldata transmission is in LTE controlled by the radio base station. Inorder to support efficient uplink scheduling, a method has been definedto inform the base station of the buffer status of the UE. This methodmainly consists of buffer status reports (BSR) and scheduling requests(SR). A number of rules have been defined regarding when a UE shouldtrigger a BSR, such as arrival of new data to an empty buffer. The BSRis sent on the physical uplink shared channel (PUCCH) like other datatransmissions.

A BSR transmission therefore requires a valid uplink resource. SR hasbeen defined as single bit information indicating to the base stationthat a BSR has been triggered in the UE. The SR can be transmittedeither on a preconfigured semi-static configured periodic resource onthe physical uplink control channel (PUCCH), referred to as D-SR, or ifno such resource has been configured, on the Random Access Channel(RACH), referred to as RA-SR. The D-SR resource on the PUCCH uses a codedivision multiple access scheme to uniquely identify the user on aspecific time/frequency resource.

On each LTE uplink resource block pair dedicated for PUCCH, up to 36unique code resources is available. A resource block pair is atime-frequency resource consisting of two in time consecutive resourceblocks made up from one slot (0.5 ms) in time and 180 kHz in frequency.Two slots make up a transmission time instance (TTI). It is up to theLTE base station, i.e., an eNodeB, to divide the resources in time,frequency and code, where the trade-off stands between shortperiodicities giving low latency but costing in larger overhead forcontrol channels versus lower overhead but with longer delay.

Thus, as described above, in LTE there is a semi-static configuration ofSR resources and no SR collisions since the SR resources are not reused.For an active session the static configuration can limit the latency andthe available bandwidth of the user. A remedy would be to configure ashorter SR periodicity, but this would limit the number of users thatcould be present in the system. Consider, as a purely illustrativeexample, that a system was configured to use 2 resource blocks for SRand that the UEs has a 1 ms SR periodicity, this would limit the systemto 72 UEs with a SR resource.

The reason for the limit in latency is the corresponding waiting periodsfor requesting UL resources. The need for uplink resources can be eitherthat the UE wishes to send data, but it can also be feedback to higherlayers. One scenario where faster feedback is important isTCP-slowstart. This a mechanism to sense the bandwidth to user by slowlyraising the transmission bandwidth, while waiting for confirmation. Thefaster the UE can give feedback, the faster the transmission will rise.The extra latency on feedback can also be interpreted by higher layersas a limit in downlink bandwidth. This can lead to throttling of thedownlink throughput, even if the LTE system could support higherbandwidth.

Accordingly, it would be desirable to provide a mechanism to reuseresources for transmitting SRs, while also being able to identify usersand resolve SR collisions, e.g., on the PUCCH in an LTE system.

SUMMARY

A method for transmitting a scheduling request (SR) on a physical uplinkcontrol channel (PUCCH) comprising:

-   -   receiving, by a user equipment, SR collision mitigation        information; and    -   transmitting an SR signal on said PUCCH using a transmission        resource which is selected based on the SR collision mitigation        information.

The SR collision mitigation information can indicate (a) a resourcepattern assigned to the UE, (b) a signal pattern assigned to the UE, or(c) a prohibition time assigned to the UE. The SR collision mitigationinformation can indicate (a) a resource to pattern assigned to the UEand (b) a signal pattern assigned to the UE. The SR collision mitigationinformation can indicate (a) a resource pattern assigned to the UE, (b)a signal pattern assigned to the UE, and (c) a prohibition time assignedto the UE. The SR collision mitigation information can indicate (a) aresource pattern assigned to the UE and (c) a prohibition time assignedto the UE. The SR collision mitigation information can indicate (b) asignal pattern assigned to the UE, and (c) a prohibition time assignedto the UE.

A user equipment (UE) comprising:

-   -   a transceiver configured to receive SR collision mitigation        information, and

further configured to transmit an SR signal on a PUCCH using atransmission resource which is selected based on the SR collisionmitigation information.

The SR collision mitigation information can indicate (a) a resourcepattern assigned to the UE, (b) a signal pattern assigned to the UE, or(c) a prohibition time assigned to the UE. The SR collision mitigationinformation can indicate (a) a resource pattern assigned to the UE and(b) a signal pattern assigned to the UE. The SR collision mitigationinformation can indicate (a) a resource pattern assigned to the UE, (b)a signal pattern assigned to the UE, and (c) a prohibition time assignedto the UE. The SR collision mitigation information can indicate (a) aresource pattern assigned to the UE and (c) a prohibition time assignedto the UE. The SR collision mitigation information can indicate (b) asignal pattern assigned to the UE, and (c) a prohibition time assignedto the UE.

A method for mitigating scheduling request (SR) collisions on a PUCCHcomprising:

transmitting, by a base station, SR collision mitigation informationtoward user equipments (UEs);

receiving, by the base station, one or more SR signals;

determining, by the base station, that an SR collision has occurred; and

resolving the SR collision based on the SR collision mitigationinformation.

The SR collision mitigation information can indicate (a) a resourcepattern assigned to the UE, (b) a signal pattern assigned to the UE, or(c) a prohibition time assigned to the UE. The SR collision mitigationinformation can indicate (a) a resource pattern assigned to the UE and(b) a signal pattern assigned to the UE. The SR collision mitigationinformation can indicate (a) a resource pattern assigned to the UE, (b)a signal pattern assigned to the UE, and (c) a prohibition time assignedto the UE. The SR collision mitigation information can indicate (a) aresource pattern assigned to the UE and (c) a prohibition time assignedto the UE. The SR collision mitigation information can indicate (b) asignal pattern assigned to the UE, and (c) a prohibition time assignedto the UE.

The base station can be an eNodeB.

A base station comprising:

a transceiver configured to transmit, by a base station, SR collisionmitigation information toward user equipments (UEs);

wherein the transceiver is further configured to receive one or more SRsignals;

a processor configured to determine that an SR collision has occurredand to resolve the SR collision based on the SR collision mitigationinformation.

The SR collision mitigation information can indicate (a) a resourcepattern assigned to the UE, (b) a signal pattern assigned to the UE, or(c) a prohibition time assigned to the UE. The SR collision mitigationinformation can indicate (a) a resource pattern assigned to the UE and(b) a signal pattern assigned to the UE. The SR collision mitigationinformation can indicate (a) a resource pattern assigned to the UE, (b)a signal pattern assigned to the UE, and (c) a prohibition time assignedto the UE. The SR collision mitigation information can indicate (a) aresource pattern assigned to the UE and (c) a prohibition time assignedto the UE. The SR collision mitigation information can indicate (b) asignal pattern assigned to the UE, and (c) a prohibition time assignedto the UE.

The base station can be an eNodeB.

A method for mitigating scheduling request (SR) collisions on a PUCCHcomprising:

receiving, by the base station, one or more SR signals;

determining, by the base station, that an SR collision has occurred;

determining, by the base station, channel signature informationassociated with the one or more SR signals; and

resolving the SR collision based on the channel signature information.

The channel signature information can be based on one or more ofpath-gain (or loss), Doppler shift and/or angle of arrival of thesignal.

The base station can be an eNodeB.

A base station comprising:

a transceiver configured to receive one or more SR signals;

a processor configured to determine that an SR collision has occurred,to determine channel signature information associated with the one ormore SR signals and to resolve the SR collision based on the channelsignature information.

The channel signature information can be based on one or more ofpath-gain (or loss), Doppler shift and/or angle of arrival of thesignal.

The base station can be an eNodeB.

These embodiments enable, among other things, reuse of SR transmissionresources to support greater numbers of geographically proximate UEs.For example, collisions of SRs which have been transmitted by differentUEs using the same SR transmission resource are reduced in the firstinstance and, to the extent that such collisions may still occur, theycan be more readily resolved. Collision resolution may occur by, forexample, using information about a UE's SR resource pattern, signalpattern, prohibition time and/or channel signature to determine which UEwas likely involved in an SR signal collision.

ABBREVIATIONS 3GPP 3^(rd) Generation Partnership Project BS Base StationBSR Buffer Status Report

eNodeB evolved Node B

LTE Long-Term Evolution PUCCH Physical Uplink Control Channel SC-FDMASingle Carrier Frequency Division Multiple Access SR Scheduling RequestUE User Equipment

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings illustrate exemplary embodiments, wherein:

FIG. 1 is a schematic diagram illustrating the LTE time-frequency grid.

FIG. 2 is a schematic diagram illustrating the LTE downlink framestructure.

FIG. 3 is a schematic diagram illustrating an LTE downlink subframe.

FIGS. 4( a)-4(c) are schematic diagrams illustrating various aspects ofLTE uplink structure;

FIG. 5 is a schematic diagram illustrating a base station and mobilestation.

FIG. 6 is a schematic diagram showing a scenario in a radiocommunications network.

FIG. 7 is a schematic diagram illustrating processing of data packets inLTE.

FIGS. 8-13 depict various aspects of SR collision interference accordingto embodiments.

FIG. 14 illustrates embodiments of a base station (or other node).

DETAILED DESCRIPTION

The following detailed description of the example embodiments refers tothe accompanying drawings. The same reference numbers in differentdrawings identify the same or similar elements. Also, the followingdetailed description does not limit the invention. The followingembodiments are discussed, for simplicity, with regard to theterminology and structure of LTE systems. However, the embodiments to bediscussed next are not limited to LTE systems but may be applied toother telecommunications systems.

Reference throughout the specification to “one embodiment” or “anembodiment” means that a particular feature, structure, orcharacteristic described in connection with an embodiment is included inat least one embodiment of the present invention. Thus, the appearanceof the phrases “in one embodiment” or “in an embodiment” in variousplaces throughout the specification are not necessarily all referring tothe same embodiment. Further, the particular features, structures orcharacteristics may be combined in any suitable manner in one or moreembodiments.

As mentioned above, it would be desirable to provide one or moremechanisms to enable the reuse of resources for transmitting schedulingrequests (SRs), while also being able to identify users and resolvecollisions, e.g., on the PUCCH in an LTE system. Various mechanisms aredescribed herein including:

(a) to assign to each user i a periodicity p(i) and a sequence ofresource indices; this is referred to herein as assignment of a resourcepattern;

(b) to assign to each user i a periodicity p(i) and a symbol sequence;this is referred to herein as assignment of a signal pattern;

(c) to assign to each user i a prohibition time t(i), that is, if user itransmits at time t, the next time the user can transmit is at timet+t(i);

(d) for each user there can be a number of reception points (e.g.,multiple antennas in the same or different eNBs) from which a predictedchannel parameter or parameters (for example path gain) can be discernedfor that user; this is referred to herein as the channel signature ofthe user.

As will be described in more detail below, each of these mechanisms canbe used by themselves or in combination with one another to provide forhigh resource reuse and high probability of collision resolution in thecontext of uplink SR transmissions. Generically, one or more of thesemechanisms which can be implemented as an embodiment are referred toherein as “SR collision mitigation mechanisms”. In this context, notethat SR collision mitigation information or mechanisms as describedherein refer generally to information or mechanisms which enable thesame SR transmission resources to be allocated to more than one UE in amanner which also facilitates resolving transmission collisions whichoccur if such UEs do, in fact, transmit SRs using the same SRtransmission resource.

To provide some context for the following example embodiments related toSR collision mitigation mechanisms, consider the example radiocommunication system as shown from two different perspectives in FIGS. 5and 6, respectively. To increase the transmission rate of the systems,and to provide additional diversity against fading on the radiochannels, modern wireless communication systems include transceiversthat use multi-antennas (often referred to as a MIMO systems). Themulti-antennas may be distributed to the receiver side, to thetransmitter side and/or provided at both sides as shown in FIG. 5. Morespecifically, FIG. 5 shows a base station 32 having four antennas 34 anda user terminal (also referred to herein as “user equipment” or “UE”) 36having two antennas 34. The number of antennas shown in FIG. 5 is anexample only, and is not intended to limit the actual number of antennasused at the base station 32 or at the user terminal 36 in the exampleembodiments to be discussed below.

Additionally, the term “base station” is used herein as a generic term.As will be appreciated by those skilled in the art, in the LTEarchitecture an evolved NodeB (eNodeB) may correspond to the basestation, i.e., a base station is a possible implementation of theeNodeB. However, the term “eNodeB” is also broader in some senses thanthe conventional base station since the eNodeB refers, in general, to alogical node. The term “base station” is used herein as inclusive of abase station, a NodeB, an eNodeB or other nodes specific for otherarchitectures. An eNodeB in an LTE system handles transmission andreception in one or several cells, as shown for example in FIG. 6.

FIG. 6 shows, among other things, two eNodeBs 32 and one user terminal36. The user terminal 36 uses dedicated channels 40 to communicate withthe eNodeB(s) 32, e.g., by transmitting or receiving RLC PDU segments asaccording to example embodiments described below. The two eNodeBs 32 areconnected to a Core Network 44.

One example LTE architecture for processing data for transmission by aneNodeB 32 to a UE 36 (downlink) is shown in FIG. 7. Therein, data to betransmitted by the eNodeB 32 (e.g., IP packets) to a particular user isfirst processed by a packet data convergence protocol (PDCP) entity 50in which the IP headers are (optionally) compressed and ciphering of thedata is performed. The radio link control (RLC) entity 52 handles, amongother things, segmentation of (and/or concatenation of) the datareceived from the PDCP entity 50 into protocol data units (PDUs).Additionally, the RLC entity 52 optionally provides a retransmissionprotocol (ARQ) which monitors sequence number status reports from itscounterpart RLC entity in the UE 36 to selectively retransmit POUs asrequested. The medium access control (MAC) entity 54 is responsible foruplink and downlink scheduling via scheduler 56, as well as thehybrid-ARQ processes discussed above. A physical (PHY) layer entity 58takes care of coding, modulation, and multi-antenna mapping, among otherthings. Each entity shown in FIG. 7 provides outputs to, and receivesinputs from, their adjacent entities by way of bearers or channels asshown. The reverse of these processes are provided for the UE 36 asshown in FIG. 7 for the received data, and the UE 36 also has similartransmit chain elements as the eNB 34 for transmitting on the uplinktoward the eNB 32, as will be described in more detail belowparticularly with respect to neighbour cell lists, measurements andmeasurement patterns.

Having described some example LTE devices in which aspects of SRcollision mitigation mechanisms according to example embodiments can beimplemented, the discussion now returns to consideration of thesecollision mitigation topics. Starting first with an example of an SRcollision mitigation mechanism of the type (a) described above, supposethat a system has N resources available for SR transmissions. In thiscontext an SR transmission resource can, for example, each include aPUCCH resource index associated with both a frequency resource and acode resource, and a time offset.

For each user i a number n(i) is selected, this number represents thenumber of resource indices assigned to user i. The network then assignsto each user i a pattern, such that if two patterns collide at time t,it is ensured that they do not collide at time t+p(i). FIG. 8 depicts apurely illustrative example of this resource pattern embodiment whereinthe pattern has parameter values of p=2, n=5 and the resource sequenceis [2,1,5,4,7]. Thus, as seen in FIG. 8, the UE which has been assignedthis exemplary resource pattern could transmit an SR signal in everyother time slot using a specified (and revolving) resource identified bya respective one of the indices 2, 1, 5, 4, 7, 2, 1, 5 . . . .

Considering next an example of an SR collision mitigation mechanism ofthe type (b) described above, i.e., associated with using a signalpattern, suppose that signals transmitted in the exemplary radiocommunication system use BPSK modulation, then a signal pattern would berepresented as a bit sequence (alternatively QPSK modulation would berepresented by two bits per symbol). For two users, the system ornetwork can assign the symbol patterns 0000 and 0101. FIG. 9 illustratesthese exemplary signal patterns associated with the two users accordingto this embodiment. Note that in this example a pair of consecutivesignals is orthogonal.

Considering next an example of an SR collision mitigation mechanism ofthe type (d) described above, i.e., associated with channel signatures,a baseline implementation of a channel or signal signature should bepossible to implement on a single eNB. Here, the concept is to use richchannel data for each UE as part of the identification and collisionresolution process, see e.g., FIG. 10. Therein, an eNB equipped withmultiple antennas can use measurements from the different antennas toestimate path-gain, Doppler shift and/or angle of arrival of the signal.This data can then be used to identify users by matching the measures tohistoric data for the candidate UEs, i.e., those UEs in proximity to theeNB which may have transmitted SRs that have collided with one anotheron the uplink by virtue of their being transmitted, e.g., using the sameSR transmission resource.

Using multiple eNBs, a more advanced solution can be provided as, forexample shown in FIG. 11. As illustrated therein, the system can use thechannel measurements, e.g., path-gain, Doppler shift and/or angle ofarrival of the signal, of the signal received by one or more of theserving cell and neighboring cells to aid in resolving SR collisions.For example, we can let the three eNBs with the highest path gain definethe channel signature; in this example we could use [C(0), C(1), C(5)]as a signal pattern for the UE in the picture (0 being the servingcell).

Having described some of the exemplary SR collision mitigationmechanisms described herein, consider now some exemplary usages thereof.Suppose that at time t a transmission is detected by the system onresource index i with a received signal S in the serving cell and E(i)to the neighboring cells. Let D(i,t) be the collection of channelsignatures of users that can use resource i at time t. ML-decoding canthen be used on S and E(i) to identify the user transmitting on theresource using the collection D(i,j) as candidates. After decoding, thesystem can conclude that it is likely that a collision has occurredbetween the SR transmissions from two (or more) UEs. Depending on, forexample load, the system can either avoid scheduling a user, or do aML-decoding for a combination of users and, for example, schedule thetwo users that have a combined channel signature best corresponding tothe received signal.

If a collision has occurred (or if the system doesn't decode the useridentity), the system can resolve the collision in the next TTI with atransmission. The system can, for example, accomplish this by using thecombined information from the signals received in the two TTIs usingML-decoding. If good resource patterns are used, e.g., as describedabove with respect to category (a), the users colliding in the first TTIwill not collide in the next TTI. If good signal patterns are used,e.g., as described above with respect to category (b), then the signalsspanning over, for example, two TTI s with collisions will beorthogonal. Even better separation between users or higher reuse can beachieved by assigning both signal and resource patterns to the users fortheir transmission of SR signals on the PUCCH. For resource patterns thesystem can use both time and index separation to make sure that thereare never two consecutive collisions, see, e.g., FIG. 8 for a timeseparation example.

Suppose that there are three categories of users which are givendifferent periodicities for SR transmission. Suppose further that thenetwork assigns p(1)=2, p(2)=3 and p(3)=5 to the three categories ofusers. Then, if there is a collision between two users there will be nocollision between the same two users in the next three TTIs withtransmissions even if a fixed resource index is used. Clearly the worstcase is a collision between users 1 and 2, see e.g., FIG. 12.

Consider next an SR collision mitigation mechanism of type (c), i.e.,including a time prohibition feature. Suppose, for example, that thereare three categories of users given the same periodicities for SRtransmission, but different prohibition times. Suppose further that thesystem assigns p(1)=p(2)=p(3)=1 and t(1)=2, t(2)=3 and t(3)=5. If thereis a collision between two users there will be no collision between thesame two users in the next three TTIs with transmissions even if a fixedresource index is used. Thus, the situation is the same in the previousexample, as illustrated in FIG. 12. Observe, however, that if the systemassigns prohibition times which are relatively prime to the resourcepattern lengths all information will be used in the resource pattern.See FIG. 13 for an example with prohibition time 2 and resource patternlength 5.

Note that all of the embodiments described herein which rely onseparation in time, resource and/or signal pattern are described onsubframe basis (TTI) but may also be applied on slot basis, where onesubframe consists of two consecutive slots.

The above described schemes provide the possibility to detect the uniqueidentity of the user transmitting an SR signal, but some ambiguity stillexists, especially before the completion of the entire pattern sequence.In these cases the eNB may elect to schedule one or a subset of thepossible users. When selecting the subset to schedule factors such asprobability from detection sequence, predictions of traffic and userquality of service requirements may be taken into account. For exampleif we have a user with very delay sensitive data with a high priorityquality of service class given an SR period of 1 ms sharing thisresource with a lower priority user with an SR period of 5 ms thescheduler may first try to schedule the high priority user, beforewaiting for the next SR instance to uniquely identify the user.

The foregoing embodiments provide, for example, an advantage of highreuse; SR signal collisions can be resolved with high probability andvery short UE waiting periods for an SR resource can be achieved.Meaning that systems and methods according to these embodiments can, forexample, without any extra resource blocks used for SR go from 10 msperiodicity to 1 ms periodicity. Moreover, by operating in this way, theexpected latency for requesting UL resources can be lowered from, e.g.,6 ms to about 2.5 ms.

Also it should be noted that even with high transmission resource reusethe risk of SR collision can be kept low. For example, suppose that asystem assigns patterns in 10 by 10 blocks, that each such block isassigned to 100 users, and that the system randomly picks patterns forthe users. Further suppose that the probability that a user wants to useone resource is 10% uniformly over this block. Then the expected numberof collisions is less than 0.47 and, if good patterns are selected, thenthis expected number of collisions would be even less.

An example base station 32, e.g., an eNodeB, which is configured tointeract with a UE as described above to mitigate SR collision impactsis generically illustrated in FIG. 14. Therein, the eNodeB 32 includesone or more antennas 71 connected to processor(s) 74 via transceiver(s)73. The processor 74 is configured to analyze and process signalsreceived over an air interface via the antennas 71, as well as thosesignals received from core network node (e.g., access gateway) via,e.g., an interface. The processor(s) 74 may also be connected to one ormore memory device(s) 76 via a bus 78. Further units or functions, notshown, for performing various operations as encoding, decoding,modulation, demodulation, encryption, scrambling, precoding, etc. mayoptionally be implemented not only as electrical components but also insoftware or a combination of these two possibilities as would beappreciated by those skilled in the art to enable the transceiver(s) 72and processor(s) 74 to process uplink and downlink signals. A similar,generic structure, e.g., including a memory device, processor(s) and atransceiver, can be used (among other things) to implement communicationnodes such as UEs 36 to receive signals and process those signals in themanner described above. Likewise the elements shown in block 32 couldalso represent a network node, albeit without the provision of an airinterface transceiver.

The above-described example embodiments are intended to be illustrativein all respects, rather than restrictive, of the present invention. Allsuch variations and modifications are considered to be within the scopeand spirit of the present invention as defined by the following claims.No element, act, or instruction used in the description of the presentapplication should be construed as critical or essential to theinvention unless explicitly described as such. Also, as used herein, thearticle “a” is intended to include one or more items.

1. A method in a user equipment (UE) for transmitting a schedulingrequester (SR) on a physical uplink control channel (PUCCH) comprising:receiving SR collision mitigation information; and transmitting an SRsignal on said PUCCH using an SR transmission resource which is selectedbased on the SR collision mitigation information.
 2. The method of claim1, wherein the SR collision mitigation information includes a resourcepattern assigned to the UE, wherein the resource pattern includes aperiodicity at which the UE is to transmit the SR signal and a sequenceof SR transmission resources on which the UE is to transmit the SRsignal.
 3. The method of claim 1, wherein the SR collision mitigationinformation includes a signal pattern assigned to the UE, wherein thesignal pattern includes a periodicity at which the UE is to transmit theSR signal and a symbol sequence which the UE is to include in the SRsignal.
 4. The method of claim 1, wherein the SR collision mitigationinformation includes a prohibition time assigned to the UE, whereinafter said UE transmits said SR signal, said UE waits for saidprohibition time to transmit said SR signal again.
 5. The method ofclaim 1, wherein the SR signal includes a single bit of informationindicating to a base station that a buffer status report (BSR) has beentriggered in the UE.
 6. The method of claim 2, wherein said SRtransmission resources each include a PUCCH resource index associatedwith both a frequency resource and a code resource, and a time offset.7. The method of claim 3, wherein said symbol sequence is based, atleast in part, on a type of modulation used to transmit the SR signal.8. The method of claim 1, further comprising: if no acknowledgement ofthe SR signal is received, then re-transmitting said SR signal inaccordance with the SR collision mitigation information.
 9. The methodof claim 8, wherein the SR collision mitigation information includes aresource pattern assigned to the UE, wherein the resource patternincludes a periodicity at which the UE is to transmit the SR signal anda sequence of SR transmission resources on which the UE is to transmitthe SR signal; and the method further comprising re-transmitting the SRsignal based on the periodicity and using a next SR transmissionresource in the sequence.
 10. The method of claim 8, wherein the SRcollision mitigation information includes a prohibition time assigned tothe UE, wherein said UE re-transmits said SR signal after waiting forsaid prohibition time to elapse.
 11. A user equipment (UE) comprising: atransceiver configured to: receive scheduling requester (SR) collisionmitigation information; and transmit an SR signal on a physical uplinkcontrol channel (PUCCH) using an SR transmission resource which isselected based on the SR collision mitigation information.
 12. The UE ofclaim 11, wherein the SR collision mitigation information includes aresource pattern assigned to the UE, wherein the resource patternincludes a periodicity at which the UE is to transmit the SR signal anda sequence of SR transmission resources on which the UE is to transmitthe SR signal.
 13. The UE of claim 11, wherein the SR collisionmitigation information includes a signal pattern assigned to the UE,wherein the signal pattern includes a periodicity at which the UE is totransmit the SR signal and a symbol sequence which the UE is to includein the SR signal.
 14. The UE of claim 11, wherein the SR collisionmitigation information includes a prohibition time assigned to the UE,wherein after said UE transmits said SR signal, said UE must then waitfor said prohibition time to transmit said SR signal again.
 15. The UEof claim 11, wherein the SR signal includes a single bit of informationindicating to a base station that a buffer status report (BSR) has beentriggered in the UE.
 16. The UE of claim 11, wherein said SRtransmission resources each include a PUCCH resource index associatedwith a frequency resource and a code resource, and a time offset. 17.The UE of claim 13, wherein said symbol sequence is based, at least inpart, on a type of modulation used to transmit the SR signal.
 18. The UEof claim 11, wherein the transceiver is further configured to: if noacknowledgement of the SR signal is received, then re-transmit said SRsignal in accordance with the SR collision mitigation information. 19.The UE of claim 18, wherein the SR collision mitigation informationincludes a resource pattern assigned to the UE, wherein the resourcepattern includes a periodicity at which the UE is to transmit the SRsignal and a sequence of SR transmission resources on which the UE is totransmit the SR signal; and the transceiver further configured tore-transmit the SR signal based on the periodicity and using a next SRtransmission resource in the sequence.
 20. The UE of claim 18, whereinthe SR collision mitigation information includes a prohibition timeassigned to the UE, wherein said transceiver is further configured tore-transmit said SR signal after waiting for said prohibition time toelapse.
 21. A method in a base station for mitigating schedulingrequester (SR) collisions on a physical uplink control channel (PUCCH)comprising: transmitting SR collision mitigation information toward userequipments (UEs); receiving at least one SR signal; determining that anSR collision has occurred; and resolving the SR collision based on theSR collision mitigation information.
 22. The method of claim 21, whereinthe resolving further comprises: identifying, based on the SR collisionmitigation information, at least one UE which was likely to havetransmitted an SR signal involved in said SR collision; and granting theat least one UE uplink transmission resources in response to theidentifying.
 23. The method of claim 21, wherein the SR collisionmitigation information includes a resource pattern assigned to the UE,wherein the resource pattern includes a periodicity at which the UE isto transmit the SR signal and a sequence of SR transmission resources onwhich the UE is to transmit the SR signal.
 24. The method of claim 21,wherein the SR collision mitigation information includes a signalpattern assigned to the UE, wherein the signal pattern includes aperiodicity at which the UE is to transmit the SR signal and a symbolsequence which the UE is to include in the SR signal.
 25. The method ofclaim 21, wherein the SR collision mitigation information includes aprohibition time assigned to the UE, wherein after said UE transmitssaid SR signal, said UE waits for said prohibition time to transmit saidSR signal again.
 26. The method of claim 21, wherein the resolvingfurther comprises: estimating, by the base station, at least one ofpath-gain, Doppler shift and angle of arrival of the at least one SRsignal; and identifying users associated with the SR collision bycomparing the estimated at least one of path-gain, Doppler shift andangle of arrival to historic data for candidate UEs.
 27. The method ofclaim 26, further comprising: receiving estimates of the at least one ofone of path-gain, Doppler shift and angle of arrival of the at least oneSR signal; and using the received estimates in the identifying step. 28.The method of claim 21, wherein the at least one SR signal includes asingle bit of information indicating to the base station that a bufferstatus report (BSR) has been triggered in a corresponding UE.
 29. A basestation comprising: a transceiver configured to: transmit, by a basestation, scheduling request (SR) collision mitigation information towarduser equipments (UEs); receive at least one SR signal; and a processorconfigured to: determine that an SR collision has occurred; and resolvethe SR collision based on the SR collision mitigation information. 30.The base station of claim 29, wherein the processor is furtherconfigured to resolve the SR collision by: identifying, based on the SRcollision mitigation information, at least one UE which was likely tohave transmitted an SR signal involved in said SR collision; andgranting the at least one UE uplink transmission resources.
 31. The basestation of claim 29, wherein the SR collision mitigation informationincludes a resource pattern assigned to the UE, wherein the resourcepattern includes a periodicity at which the UE is to transmit the SRsignal and a sequence of SR transmission resources on which the UE is totransmit the SR signal.
 32. The base station of claim 29, wherein the SRcollision mitigation information includes a signal pattern assigned tothe UE, wherein the signal pattern includes a periodicity at which theUE is to transmit the SR signal and a symbol sequence which the UE is toinclude in the SR signal.
 33. The base station of claim 29, wherein theSR collision mitigation information includes a prohibition time assignedto the UE, wherein after said UE transmits said SR signal, said UE waitsfor said prohibition time to transmit said SR signal again.
 34. The basestation of claim 29, wherein the processor is further configured to:resolve the SR collision by estimating, by the base station, at leastone of path-gain, Doppler shift and angle of arrival of the one or moreSR signals; and identify users associated with the SR collision bycomparing the estimated at least one of path-gain, Doppler shift andangle of arrival to historic data for candidate UEs.
 35. The basestation of claim 34, further comprising an interface configured toreceive estimates of the at least one of one of path-gain, Doppler shiftand angle of arrival of the at least one SR signal from other basestations; and the processor is further configured to identify the usersusing the received estimates.
 36. The base station of claim 29, whereinthe at least one SR signal includes a single bit of informationindicating to the base station that a buffer status report (BSR) hasbeen triggered in a corresponding UE.